Image Reconstruction Of Defects In Eddy Current Nondestructive Testing

With the continuous development of industry in countries, thus nondestructive testing as an integral and effective tool of industrial development gets more attention. Nondestructive testing is a detection technology, which uses the light, sound and electromagnetic principle features of objects to detect defects, chemical and physical parameters of parts, materials and equipment. There are many methods of nondestructive testing on account of different application fields and detection principle. Electromagnetic detection technology is an important branch of nondestructive testing. It is a preferred method of implementing surface detection in conductive workpiece and ferromagnetic materials with the advantages of high detection sensitivity, high efficiency and simple and convenient signal coupling.Eddy current testing technique, one kind of electromagnetic detection, is a nondestructive testing method based on the principle of electromagnetic induction. Eddy current testing is so widespread due to non-contact measurement, coupling-agent-free, high sensitivity in surface detection, that many scholars at home and abroad spend a lot of fund and energy researching on the qualitative detection and the quantitative detection of defects using eddy current. But so far, eddy current testing equipment is operated by professionals passing the professional test. And almost no one device can be used by more professionals and non-professionals, which can clearly and directly display defect graphics. So it is a difficulty and focus of research for correlative researchers.Through deeply analyzing the status quo and the existing problems of eddy current testing, this topic puts forward two algorithms on the basis of the existing technology, which can be used to reconstruct the magnetic induction intensity values of the tested points according to the measured magnetic field signals and display defect graphics in real time. So this topic tries to solve the inconveniences that testers determine defects indirectly only by analyzing the magnetic field waveform figure or other data.This paper firstly introduces the features and the research status of eddy current testing at home and abroad, secondly analyses the basic principle of eddy current testing, finally designs a set of eddy current testing system. This system mainly consists of three parts: probe detection, probe location, defect reconstruction. The main difference is the design of probe composed by three differential coils that can accurately obtain eddy current magnetic field data in the probe detection part. Probe location uses a video camera to locate, and this paper concretely introduces the positioning process in this part. Defect reconstruction part is the core of this topic, puts forward the normalization and hierarchical weighted defect reconstruction algorithms and compares them. Theoretically, defects should be restored well according to these two algorithms. However, in the practical test, the number of selected data point is limited due to the limitation of operation speed and testing requirements, and the detected signals have a great noise, so the reconstructed images are not obvious. Further in-depth study is necessary to display the defects clearly.At the end of this paper, all the research work in this project is summarized, some of the problems unsolved are analyzed, and some suggestion is proposed for subsequent research. Eddy current nondestructive testing technology has wide application prospect at home and abroad. This subject puts forward a new solution in the inverse problem of eddy current testing. It is the first step in fabricating prototype and has great significance in the new research direction for eddy current testing technique.